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<h1><a name="ApacheFelixShellService-ApacheFelixShellService"></a>Apache Felix Shell Service</h1>

<ul>
    <li><a href="#ApacheFelixShellService-overview" title="overview on Apache Felix Shell Service">Overview</a></li>
    <li><a href="#ApacheFelixShellService-service" title="service on Apache Felix Shell Service">How the Shell Service
        Works</a></li>
    <li><a href="#ApacheFelixShellService-commands" title="commands on Apache Felix Shell Service">How Commands Work</a>
    </li>
    <li><a href="#ApacheFelixShellService-creating" title="creating on Apache Felix Shell Service">Creating a
        Command</a></li>
    <li><a href="#ApacheFelixShellService-security" title="security on Apache Felix Shell Service">Security and the
        Shell Service</a></li>
    <li><a href="#ApacheFelixShellService-feedback" title="feedback on Apache Felix Shell Service">Feedback</a></li>
</ul>


<p><a name="ApacheFelixShellService-overview"></a></p>

<h2><a name="ApacheFelixShellService-Overview"></a>Overview</h2>

<p>In order to interact with Felix it is necessary to have some sort of
    interactive shell that allows you to issue commands to the framework
    and to obtain information from it. The OSGi specification does not
    define how an OSGi framework should provide this interactivity. Felix
    defines a shell service for creating and executing arbitrary commands.
    The shell service does not define a user interface, only a service API.</p>

<p>The benefit of the Felix shell service approach is that it is possible to:</p>

<ul>
    <li>have multiple shell user interfaces (e.g., textual and graphical),</li>
    <li>add custom commands to the shell (i.e., bundles can make commands available via the shell service), and</li>
    <li>use the shell service from other bundles/services.</li>
</ul>


<p>The remainder of this document describes how the shell service works
    and how to create custom commands for it. This document does not
    describe how to use the command shell, nor does it describe the
    text-based or GUI-based user interfaces that are available for the
    shell.</p>

<p><a name="ApacheFelixShellService-service"></a></p>

<h2><a name="ApacheFelixShellService-HowtheShellServiceWorks"></a>How the Shell Service Works</h2>

<p>The Felix shell service is intended to be a simple, but extensible
    shell service that can have multiple user interface implementations,
    all of which are independent from the Felix framework. The shell
    service is currently not intended to be sophisticated, rather it is
    just a mechanism to execute commands. The shell service maintains a
    list of command services, each of which have a unique command name. The
    shell service is defined by the following service interface:</p>

<div class="code">
    <div class="codeContent">
<pre class="code-java"><span class="code-keyword">package</span> org.apache.felix.shell;

<span class="code-keyword">public</span> <span class="code-keyword">interface</span> ShellService
{
    <span class="code-keyword">public</span> <span class="code-object">String</span>[] getCommands();
    <span class="code-keyword">public</span> <span class="code-object">String</span> getCommandUsage(<span
            class="code-object">String</span> name);
    <span class="code-keyword">public</span> <span class="code-object">String</span> getCommandDescription(<span
            class="code-object">String</span> name);
    <span class="code-keyword">public</span> ServiceReference getCommandReference(<span
            class="code-object">String</span> name);
    <span class="code-keyword">public</span> void executeCommand(
        <span class="code-object">String</span> commandLine, PrintStream out, PrintStream err)
        <span class="code-keyword">throws</span> Exception;
}</pre>
    </div>
</div>

<p>Using the shell service interface, it is possible to access and
    execute available commands. The shell service methods perform the
    following functions:</p>

<ul>
    <li><tt>getCommands()</tt> - returns an array of strings that correspond to the names of the installed shell
        commands.
    </li>
    <li><tt>getCommandUsage()</tt> - returns the command usage string for a particular command name</li>
    <li><tt>getCommandDescription()</tt> - returns a short description for a particular command name.</li>
    <li><tt>getCommandReference()</tt> - returns the service reference for a particular command name.</li>
    <li><tt>executeCommand()</tt> - executes a particular command using the specified command line and print streams.
    </li>
</ul>


<p>Most of the shell service methods require no explanation except for
    the executeCommand() method. Even though this method is the most
    complex, it is still fairly simplistic. The assumption of the shell
    service is that a command line will be typed by the user (or perhaps
    constructed by a GUI) and passed into it for execution. The shell
    service interprets the command line in a very simplistic fashion; it
    takes the leading string of characters terminated by a space character
    (not including it) and assumes that this leading token is the command
    name. Consider the following command line:</p>

<div class="preformatted">
    <div class="preformattedContent">
<pre>update 3 http://www.foo.com/bar.jar
</pre>
    </div>
</div>

<p>The shell service interprets this as an <tt>update</tt> command and
    will search for a command service with the same name. If a
    corresponding command service is not found, then it will print an error
    message to the error print stream. If a corresponding command service
    is found, then it will pass the entire command line string and the
    print streams into the <tt>executeCommand()</tt> method of the command service (for a more detailed description of
    command services, see the next section).</p>

<p>Notice that there is no method to add commands to the shell service
    interface. This is because commands are implemented as OSGi services
    and the shell service listens for service events and when a command
    service registers/unregisters it automatically updates its list of
    commands accordingly.</p>

<p><a name="ApacheFelixShellService-commands"></a></p>

<h2><a name="ApacheFelixShellService-HowCommandsWork"></a>How Commands Work</h2>

<p>All commands available in the shell service are implemented as OSGi
    services. The advantage of this approach is two-fold: the shell service
    can leverage OSGi service events to maintain its list of available
    commands and the set available commands is dynamically extendable by
    installed bundles. The command service interface is defined as follows:</p>

<div class="code">
    <div class="codeContent">
<pre class="code-java"><span class="code-keyword">package</span> org.ungoverned.osgi.service.shell;

<span class="code-keyword">public</span> <span class="code-keyword">interface</span> Command
{
    <span class="code-keyword">public</span> <span class="code-object">String</span> getName();
    <span class="code-keyword">public</span> <span class="code-object">String</span> getUsage();
    <span class="code-keyword">public</span> <span class="code-object">String</span> getShortDescription();
    <span class="code-keyword">public</span> void execute(<span class="code-object">String</span> line, PrintStream out, PrintStream err);
}</pre>
    </div>
</div>

<p>The semantics of the command service methods are:</p>

<ul>
    <li><tt>getName()</tt> - returns the name of the command; this must not contain whitespace and must be unique.</li>
    <li><tt>getUsage()</tt>
        - returns the usage string of the command; this should be one line and
        as short as possible (this is used for generating the help command
        output).
    </li>
    <li><tt>getShortDescription()</tt> - returns a short
        description of the command; this should be one line and as short as
        possible (this is used for generating the help command output).
    </li>
    <li><tt>execute()</tt> - executes the command's functionality using supplied command line and print streams.</li>
</ul>


<p><a name="ApacheFelixShellService-creating"></a></p>

<h2><a name="ApacheFelixShellService-CreatingaCommand"></a>Creating a Command</h2>

<p>The following example creates a simple version of the <tt>start</tt> command.</p>

<div class="code">
    <div class="codeContent">
<pre class="code-java"><span class="code-keyword">package</span> test;

<span class="code-keyword">import</span> java.io.PrintStream;
<span class="code-keyword">import</span> java.net.URL;
<span class="code-keyword">import</span> java.net.MalformedURLException;
<span class="code-keyword">import</span> java.util.StringTokenizer;

<span class="code-keyword">import</span> org.osgi.framework.*;
<span class="code-keyword">import</span> org.apache.felix.shell.ShellService;
<span class="code-keyword">import</span> org.apache.felix.shell.Command;

<span class="code-keyword">public</span> class MyStartCommandImpl <span class="code-keyword">implements</span> Command
{
    <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;

    <span class="code-keyword">public</span> MyStartCommandImpl(BundleContext context)
    {
        m_context = context;
    }

    <span class="code-keyword">public</span> <span class="code-object">String</span> getName()
    {
        <span class="code-keyword">return</span> <span class="code-quote">"mystart"</span>;
    }

    <span class="code-keyword">public</span> <span class="code-object">String</span> getUsage()
    {
        <span class="code-keyword">return</span> <span class="code-quote">"mystart &lt;id&gt; [&lt;id&gt; ...]"</span>;
    }

    <span class="code-keyword">public</span> <span class="code-object">String</span> getShortDescription()
    {
        <span class="code-keyword">return</span> <span class="code-quote">"start bundle(s)."</span>;
    }

    <span class="code-keyword">public</span> void execute(<span class="code-object">String</span> s, PrintStream out, PrintStream err)
    {
        StringTokenizer st = <span class="code-keyword">new</span> StringTokenizer(s, <span
            class="code-quote">" "</span>);

        <span class="code-comment">// Ignore the command name.
</span>        st.nextToken();

        <span class="code-comment">// There should be at least one bundle id.
</span>        <span class="code-keyword">if</span> (st.countTokens() &gt;= 1)
        {
            <span class="code-keyword">while</span> (st.hasMoreTokens())
            {
                <span class="code-object">String</span> id = st.nextToken().trim();

                <span class="code-keyword">try</span> {
                    <span class="code-object">long</span> l = <span class="code-object">Long</span>.valueOf(id).longValue();
                    Bundle bundle = m_context.getBundle(l);
                    <span class="code-keyword">if</span> (bundle != <span class="code-keyword">null</span>)
                    {
                        bundle.start();
                    }
                    <span class="code-keyword">else</span>
                    {
                        err.println(<span class="code-quote">"Bundle ID "</span> + id + <span class="code-quote">" is invalid."</span>);
                    }
                } <span class="code-keyword">catch</span> (NumberFormatException ex) {
                    err.println(<span class="code-quote">"Unable to parse id '"</span> + id + <span class="code-quote">"'."</span>);
                } <span class="code-keyword">catch</span> (BundleException ex) {
                    <span class="code-keyword">if</span> (ex.getNestedException() != <span
            class="code-keyword">null</span>)
                        err.println(ex.getNestedException().toString());
                    <span class="code-keyword">else</span>
                        err.println(ex.toString());
                } <span class="code-keyword">catch</span> (Exception ex) {
                    err.println(ex.toString());
                }
            }
        }
        <span class="code-keyword">else</span>
        {
            err.println(<span class="code-quote">"Incorrect number of arguments"</span>);
        }
    }
}</pre>
    </div>
</div>

<p>A bundle activator class is needed for packaging the command servce; the bundle activator registers the command
    service in its <tt>start()</tt> method. Note: You do not need one activator per command, a single activator can
    register any number of commands.</p>

<div class="code">
    <div class="codeContent">
<pre class="code-java"><span class="code-keyword">package</span> test;

<span class="code-keyword">import</span> org.osgi.framework.BundleActivator;
<span class="code-keyword">import</span> org.osgi.framework.BundleContext;

<span class="code-keyword">public</span> class MyStartActivator <span class="code-keyword">implements</span> BundleActivator
{
    <span class="code-keyword">private</span> <span
            class="code-keyword">transient</span> BundleContext m_context = <span class="code-keyword">null</span>;

    <span class="code-keyword">public</span> void start(BundleContext context)
    {
        m_context = context;

        <span class="code-comment">// Register the command service.
</span>        context.registerService(
            org.apache.felix.shell.Command.class.getName(),
            <span class="code-keyword">new</span> MyStartCommandImpl(m_context), <span class="code-keyword">null</span>);
    }

    <span class="code-keyword">public</span> void stop(BundleContext context)
    {
        <span class="code-comment">// Services are automatically unregistered so
</span>        <span class="code-comment">// we don't have to unregister the factory here.
</span>    }
}</pre>
    </div>
</div>

<p>To compile these classes you will need to have the <tt>framework.jar</tt> file on your class path. Compile all of the
    source files using a command like:</p>

<div class="preformatted">
    <div class="preformattedContent">
<pre>java -d c:\classes *.java
</pre>
    </div>
</div>

<p>This command compiles all of the source files and outputs the generated class files into a subdirectory of the <tt>c:\classes</tt>
    directory, called test, named after the package of the source files; for the above command to work, the <tt>c:\classes</tt>
    directory must exist. Once you have compiled all of the above classes,
    you need to create a bundle JAR file of the generated package
    directory. The bundle JAR file needs a manifest, so create a file
    called <tt>manifest.mf</tt> with the following contents:</p>

<div class="code">
    <div class="codeContent">
<pre class="code-java">Bundle-Name: My Start Command
Bundle-Description: A 'start' command <span class="code-keyword">for</span> the shell service.
Bundle-Activator: test.MyStartActivator
Bundle-ClassPath: .
Import-Package: org.apache.felix.shell</pre>
    </div>
</div>

<p>To create the bundle JAR file, issue the command:</p>

<div class="preformatted">
    <div class="preformattedContent">
<pre>jar cfm mystart.jar manifest.mf -C c:\classes test
</pre>
    </div>
</div>

<p>This command creates a JAR file using the manifest you created and
    includes all of the classes in the test directory inside of the <tt>c:\classes</tt>
    directory. Once the bundle JAR file is created, you are ready to add
    the command service to the shell service; simply start Felix and
    install and start the bundle created by the above command. By doing so,
    the new <tt>mystart</tt> command is made available via the shell service.</p>

<p><a name="ApacheFelixShellService-security"></a></p>

<h2><a name="ApacheFelixShellService-SecurityandtheShellService"></a>Security and the Shell Service</h2>

<p>The shell service security handling is quite simple, all security is
    handled by the standard OSGi framework mechanisms. For example, if a
    bundle should not be able to register a shell service, then it should
    not be given the corresponding service permission. Security handling
    may change in future release after some experience is gained through
    usage.</p>

<p><a name="ApacheFelixShellService-feedback"></a></p>

<h2><a name="ApacheFelixShellService-Feedback"></a>Feedback</h2>

<p>Subscribe to the Felix users mailing list by sending a message to <span class="nobr"><a
        href="mailto:users-subscribe@felix.apache.org" title="Send mail to users-subscribe@felix.apache.org"
        rel="nofollow">users-subscribe@felix.apache.org<sup><img class="rendericon"
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                                                                 alt="" align="absmiddle" border="0" height="12"
                                                                 width="13"></sup></a></span>; after subscribing, email
    questions or feedback to <span class="nobr"><a href="mailto:users@felix.apache.org"
                                                   title="Send mail to users@felix.apache.org" rel="nofollow">users@felix.apache.org<sup><img
            class="rendericon" src="apache-felix-shell-service_files/mail_small.gif" alt="" align="absmiddle" border="0"
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